We studied 65 children with acute brain injury to determine how the risk of infectious complications changed with duration of intracranial pressure (ICP) monitoring. More than half of the 72 monitors inserted in these patients were in place at least 7 days (range 1 to 28). Nine infections occurred on days 2 through 11. The overall risk was 1.5 infections per 100 monitor-days. After day 6 the risk of subsequent infection diminished, as did the percent of monitors which subsequently became infected. The declining risk of infection over time suggests that infection is introduced at the time of monitor insertion. These findings justify a protocol in which a single ICP monitoring device is used as long as necessary, with reinsertion of a new monitor only if a malfunction occurs, or if daily surveillance cultures demonstrate an infection. Routine reinsertion of a new monitor might increase risk by unnecessarily re-exposing the patient to contamination at the time of insertion.